This invention relates generally to the field of saws and, more particularly, to a device for attachment to a portable power chain saw or the like for improving its operation and safety.
It is well known that portable power chain saws create a substantial risk of injury to the user, especially if improperly or carelessly used. The hazards relate primarily to the exposed nature of the chain moving along the guide bar. The fact that chain saws are basically hand tools whose control is often left to the strength and skill of the operator makes them especially dangerous. This is particularly so when it is considered that the very purpose of chain saws often relegate their use to less than ideal environments, such as wooded areas where dense and damp underbrush with rugged terrain and other inclement conditions often prevent the operator from obtaining the necessary leverage to exert sufficient control over the saw.
One of the most dangerous aspects of chain saw operation involves what is known as "kickback". Kickback may be a rapid movement of the saw which can occur as a result of careless operation of the saw. Kickback is an inherent phenomenon in chain saws which may occur when contact with another object is made by the moving chain as the chain moves around the nose of the guide bar. When kickback occurs, the saw may violently kick back from the object being cut and possibly result in severe injury to the operator.
Another potential danger associated with chain saws is the vibration emitted therefrom during operation. It has been reported that vibration from hand-held tools such as chain saws can contribute to a condition known as Raynaud's Syndrone. Symptons may include tingling, numbness and blanching of the fingers.
There have been many attempts in the prior art to improve the safety of chain saws, including some intended to prevent the conditions for kickback from occurring or minimizing the effects of kickback. These attempts sometimes involved the addition of various guards and automatic braking mechanisms to the saw. For example, U.S. Pat. No. 4,193,193 to Holzworth discloses a guard which extends from the motor housing along the top of the guide bar above the chain and down over the nose of the saw. While the guard may prevent inadvertent contact with the moving chain along the top of the guide bar, such a guard, however, precludes use of the vitally needed upper cutting surface of the saw.
Braking devices also have limitations in that they do not prevent kickback from occurring and do not significantly halt the motion of the chain after kickback has occurred. Thus, the operator may still be violently struck and seriously injured with the sharp chain even if the brake timely engages. Brakes are also relatively expensive and may cause damage to the saw. Further, it is difficult and impractical for the effectiveness of breaking devices to be measured by an operator who is relying on such a device to prevent injury in the event of kickback.
Other efforts to provide a safer chain saw have included various designs of the saw chain and guide bar. These measures also have significant practical drawbacks in that the result is that the saw is often less efficient and less capable of performing the tasks for which it is needed. Such designs of the saw chain, for example, are diminished by use of the saw or defeated by filing of the chain.
Although safety devices customarily add weight and expense and often result in some loss of utility, the ideal safety device for a chain saw should have the following characteristics. The device should:
1. make the saw safer to operate; PA1 2. not result in significant loss of utility; PA1 3. not significantly increase the weight of the saw; PA1 4. not significantly increase the expense of the saw; PA1 5. add new utility to offset any added weight, expense or loss of old utility (thereby discouraging removal); PA1 6. make the saw easier to operate with less operator fatigue; and PA1 7. not be diminished by use or defeated by operator action.
While the chain saw safety devices known in the prior art meet some of the above characteristics, they remain deficient in most areas.
Even with the various safety devices of the prior art, chain saws are still extremely dangerous to operate due to the problems associated with the operator not having full control over the saw at all times. The difficulty in maintaining control is primarily related to the unsecured tip of the saw. While the operator may be able to maintain fairly good control over the motor end of the saw, where the handles are located, complete control is not possible without means for directly controlling the saw tip. This is especially important in situations where the danger of kickback is present. Therefore, in order to efficiently maximize control over a chain saw, means must be provided to stabilize the saw tip with the objective being to satisfy the aforementioned characteristics that the ideal safety device should have.